Decrescendo timing control



y 1935 .11. H. HAMMOND, JR

DECRESCENDO TIMING CONTROL Filed Jan. 11, 1933 mm we INVENTO ATTORNEYS Patented July 23, 1935 UNITED STATES PATENT OFFICZE Application January 11,

18 Claims.

The invention relates to phonographic reproduction of speech and music, and more particularly to a system for improving the quality of the reproduced selection.

The invention, in one form, relates to electric reproduction of phonograph discs or talking films utilizing a dynamic multiplier by which the volume ratio of the reproduced sound is increased so that the reproductionis rendered more nearly in accord with the selection as originally rendered for recording purposes. In such. reproducing systems when the volume of sound is suddenly decreased or stopped altogether on the record, the low decrement of the ordinary dynamic multiplier circuit prevents the circuit from instantly following and produces a time lag or hangover which is sometimes objectionable.

According to the invention provision is made for decreasing the lag or delay in dynamic control on decrescendo. By the invention, when a signal is suddenly decreased in volume, the dynamic multiplier circuit operates to substantially immediately decrease the gain ratio of the amplifier so that the lag 01' hold over effect is greatly reduced or eliminated.

This is accomplished in one form of the invention by a space discharge device which acts as a variable resistor which varies in accordance with the signal intensity and which is in parallel with the control resistor of the dynamic multiplier and causes a rapid discharge of the condenser which is shunted across this resistor, when the input signal from the sound record suddenly falls to a low value.

The invention also consists in certain new and original features of construction and combinations of parts hereinafter set forth and claimed.

Although the novel features which are believed to be characteristic of this invention will be par ticularly pointed out in the claims appended hereto, the invention itself, as to its objects and advantages, the mode of its operation and the manner of its organization may be better understood by referring to the following drawing forming a part thereof, in which Fig. 1 illustrates diagrammatically one type of circuit for carrying out the present invention.

Fig. 2 shows curves illustrating the operation of a system constructed in accordance with the present invention.

In the followingdescription and in the claims, parts will be identified by specific names for convenience, but they are intended to be as generic in their application to similar parts as the art will permit.

1933, Serial No. 651,088

Referring more particularly to the drawing, Fig. 1 shows an amplifying system which receives its energy from a phonograph pick-up ill, or a photoelectric cell M. This cell receives light from a lamp 62 which is energized from a source 5 of power E3. The light from this lamp is focused by a lens is through an aperture H5, in an aperture plate It, upon the sound record of the moving film i l. The light which passes through this film is then focused upon the photoelectric cell H by means of a lens 58.

This cell is connected through a transformer 59 to two'contacts 2i of a double-pole doublethrow switch 22, the other contacts 23 of which are connected to the phonograph pick-up it. The blades of the switch 22 are connected through a transformer 123 to the input circuit of a space discharge device 25 constituting the main amplifier in the grid return of which is a battery fi l, and a resistance 25, shunted by a condenser 25. This resistance is also across the plate circuit of a space discharge device 2'? for decresendo control which is provided with filament battery 28 and plate battery 2%.

The secondary of the transformer 523 is connected through a condenser 38 to the input circuit of a dynamic control space discharge device 32 in the grid return of which is a resistance 33 and a biasing battery St. A battery 35 heats the filaments of the devices 2 and 32. The output circuit of the dynamic control device 32 is connected through the primary of a transformer 36. This transformer is prov ded with two secondaries 31 and 38. The secondary at is connected through a rectifier 39 to the resistance 25 and the secondary 38 is connected through a rectifier M to the input circuit of the decrescendo control device 2?. Across this input circuit is a resistance 42 shunted by a condenser 43, so chosen as to be of low time constant. A biasing battery 34 is also provided in this circuit. The potentials of batteries 29 and M may be positive or negative or zero depending upon tube characteristics, and may be suitably chosen to give proper operation of the system. The directions of windings 31 and 38 may, if desired, be so chosen as to produce opposite effects as regards production of low frequency currents in control resistor 25.

The output circuit of the device 24 includes the primary of a transformer l5 which is shunted by a resistance 46. The secondary of this transformer is connected to the input circuit of a. push-pull amplifier 4'! the output circuit of which is connected through a transformer 48 to the 65 moving coil of a loud speaker 49. The field winding 5| of this loud speaker is energized by a battery 52.

In the operation of the invention, when it is desired to use the phonograph, the switch 22 is thrown down and when it is desired to use the photographic sound record I1, the switch 22 is thrown up. In either case, energy is fed to the transformer I23 from the secondary of which it passes to the input circuit of the main amplifier device 24. Part of the energy passes through the condenser 3| to the dynamic control device 32 where it is amplified and passes through the transformer 36. The current in the secondary 31 is then rectified by the rectifier 39 and passes through the biasing-resistance 25 in the direction of the arrow thus producing a potential drop across this resistance which is proportional to the current fiowing through it, and therefore to the average input signal strength as picked up by thepick-ups ID or II. This potential drop is through the resistance 42 in the direction of the arrow, thus producing a potential drop across this resistance which is also proportional to the input signal strength. This potential is impressed upon the grid of the decrescendo control device 21 which is thereby made more negative with increased signal strength thus increasing its impedance The device 2I acts as a direct current resistance which varies in accordance with the average signal strength, being large for high signal strengths and small for weak signals. Thus, with no signal, the bias on this device is only that imposed by the battery 44 which will allow considerable current to leak through, say for example, ten times the amount passing through the resistance 25. With increasing signal strength, the bias on this device is increased, as already described, so that the current passing through the device 21 is decreased until at medium or maximum signal input to the system practically no current passes through it. The

condition, therefore, at the time of high signal strengthis that the impedance of the device 21 is very high and that both condensers 26 and 43 are fully charged.

On a rapid decrescendo, the condenser 43 discharges quickly through the resistance 42 due to the small time constant of this circuit. This quickly reduces the bias on the grid of the device 21 thus rapidly decreasing its resistance so that the condenser 26 discharges quickly through this device, thus quickly reducing the potential drop across the resistance 25 which in turn rapidly decreases the bias on the grid of the device 24. This produces a rapid decrease of the time constant of this device as shown by the curve 53 in Fig. 2 as compared with the curve 54 which is that of the normal operation of a dynamic multiplier. As above indicated, the constants of the circuit including the condenser 43 and the resistance 42 are such as to give a small time lag.

The output of the device 24 then passes through the transformer 45, the resistance 46 opera g to make the amplitude characteristics independent speaker 49 where it is reproduced as speech or music in the usual manner.

It will be noted that Fig. 2 illustrates the gain ratio of the main amplifier stage including tube 24, plotted as a function of time. Curve 54 illustrates the normal dynamic multiplier action without the benefit of the invention. As shown, it takes an appreciable time for the gain ratio to decrease when the signal intensity is suddenly cut to zero. Curve 53, on the other hand, illustrates the decrease of gain ratio with respect to time when the dynamic multiplier is provided with the decrescendo control according to the invention. It will be noted from these curves that the time for the gain ratio to decrease to a given comparatively small value is greatly decreased by the use of the invention.

It is thus seen that with this device it is possible to control the time constant of decrescendo of a dynamic multiplier preventing any undesirable time lag or hangover.

When the signal is suddenly cut off or a loud signal is suddenly diminished on the record, such as may take place in a vocal or orchestral selection on diminuendo or decrescendo, the gain ratio of the main amplifier 24 decreases very rapidly due to the use of the decrescendo control.

The appreciable lag in decrease in grain ratio of the main amplifier due to the time it would take the condenser 26 normally to discharge without the invention, often causes an unpleasant effect, displaying itself in the form of relatively loud needle scratch or film noise held over and reproduced during the beginning of a silent period on the record. Also in the case of a rapid decrescendo from a large to a small volume on the record, the lag of the dynamic multiplier causes the effect of this decrescendo to be reproduced late without, of course, any delay in the tonal reproduction proper. By the invention these unpleasant defects are eliminated.

Although only a few of the various forms in which this invention may be embodied have been shown herein, it is to be understood that the invention is not limited to any specific construction, but might be embodied in various forms without departing from the spirit of the invention or the scope of the appended claims.

What is claimed is:

1. In a sound reproducing system, a sound record, a pick-up device therefor, a main amplifier fed by said pick-up device, a sound propagating device fed by said main amplifier, a control circuit having an energy averaging device for changing the gain ratio of said main amplifier with change in average energy picked up from said record, and means also controlled by the average energy for decreasing the energyholdover by said averaging device with rapid change in a verage energy picked up from said record.

2. In a sound reproducing system, a sound record, a pick-up device therefor, a main amplifier fed by said pick-up device, a sound propagating device fed by said main amplifier, a control circuit having an energy averaging device for increasing the gain ratio of said main amplifier with increase in average energy picked up from said record, and means also controlled by the average energy for decreasing the energy holdover by said energy averaging device on decrescendo.

3. In a sound reproducing system, a sound record, a pick-up device therefor, a main amplifier fed by said pick-up device, a sound propagating device fed by said main amplifier, a control circuit having a variable control resistance and a timing capacitance thereacross for determining the gain ratio of said main amplifier, means for increasing the potential across said capacitance with increase in average energy picked up from said-record, means for increasing the value of said variable resistance with increase in average energy picked up from said record, and vice versa. and means for controlling the gain ratio of said main amplifier by said variable control resistance.

4. In a sound reproducing system, a sound record, a pick-up device therefor, a main amplifier fed by saidpick-up device, a sound propagating device fed by said main'amplifier, a control circuit fed by said pick-up device, a dynamic control resistance and a rectifier in series therewith in said control circuit, a timing condenser across said resistance, an auxiliary control circuit also fed by said pick-up device, a decrescendo control tube having its plate circuit across said timing condenser, said second control circuit having a rectifier for impressing a rectified control current on the grid of said decrescendo tube, and means for controlling the gain ratio of said main amplifier by said control resistance.

5. In a sound reproducing system, a sound record, a pick-up device therefor, a main amplifier fed by said pick-up device, a sound propagating device fed by said main amplifier, a control circuit having a dynamic control resistance and a timing capacitance thereacross for determining the gain ratio of said main amplifier, a variable resistance across said capacitance, means for increasing the potential across said capacitance with increase in average energy picked up from said record, and means for increasing the value of said variable resistance with increase in average energy picked up from said record, the value of said variable resistance dropping more rapidly with decrease in average energy than said capacitance would normally discharge through said control resistance.

6. In a sound reproducing system, a sound record, a pick-up device therefor, a main amplifier fed by said pick-up device, a sound propagating device fed by said main amplifier, a control circuit also fed by said pick-up device and having a control amplifier therein, a transformer fed by said control amplifier, said transformer having two secondaries, a main control circuit fed by one of said secondaries, an auxiliary control circuit fed by the other of said secondaries, said main control circuit having a main biasing resistance and a timing condenser across said resistance both in series with a rectifier, a decrescendo amplifier tube having its plate circuit also across said biasing resistance, said auxiliary control circuit feeding the input circuit of said decrescendo tube, a decrescendo resistance and condenser across said decrescendo input and a rectifier in series with said auxiliary control circuit, said main biasing resistance determining the gain ratio of said main amplifier.

7. In a sound reproducing system, a sound record, a pick-up device therefor, an amplifier fed by said pick-up device, a sound propagating device fed by said amplifier, means for varying the amplification of said amplifier in accordance with average energy picked up by said pickup device, and means for decreasing the effectiveness of said first means responsive to a decrease in said average energy.

8, In a sound reproducing. system, a sound record, a pick-up device therefor, an amplifier fed by said pick-up device, asound propagating device fed by said amplifier, means forvarying the amplification of said amplifier in accordance with the average energypicked up by. said pick-up device and additional means for'varying the effectiveness of said first means in accord ance with said average energy.

9. In a sound reproducing system, a. sound record, a pick-up device therefor, an amplifier fed by said pick-up device, a sound propagat ing device fed by said amplifier, means for controlling the amplification of said amplifier in accordance with the average energy picked up by said pick-up device, a device for-varying the effectiveness of said means in accordance with said average energy and means to give said device a quicker response than said control means.

10. In a sound reproducing system, a sound record, a pick-up device therefor, a vacuum tube amplifier fed by said pick-up device, a sound propagating device fed by said amplifier, means coupled with the grid circuit of said amplifier for varying the grid potential thereof in accordance with the average energy picked up by said pickup device and means for decreasing said coupling responsive to a decrease in said average energy.

11. In a sound reproducing system, a sound record, a pick-up device therefor, a vacuum tube amplifier fed by said pick-up device, a sound propagating device fed by said amplifier, a resistance shunted by a condenser in the grid circuit of said amplifier, means for passing direct current through said resistance in proportion to the average intensity of the energy pick-up, and a variable resistance shunt across said first resistance and controlled by said energy pick-up.

12. In a sound reproducing system, a sound record, a pick-up device therefor, a vacuum tube amplifier fed bysaid pick-up device, a sound propagating device fed by said amplifier, a resistance shunted by a condenser in the grid circuit of said amplifier, means for passing direct current through said resistance in proportion to the average intensity of the energy pick-up, and a three-element vacuum tube shunt across said resistance.

13. In a sound reproducing system, a sound record, a pick-up device therefor, a vacuum tube amplifier fed by said pick-up device, a sound propagating device fed by said amplifier, a resistance shunted by a condenser in the grid circuit of the said amplifier, means for passing direct current through said resistance in proportion to the average intensity of the energy pick-up, a vacuum tube shunt across said resistance and means for controlling the grid of said tube.

14. In a sound record system, a transducer, a control channel for varying the energy transfer ratio of said transducer according to a moving average of the input energy, and means for governing the lag in the operation of said control channel.

15. In a sound record system, a transducer,a control channel for varying the energy transfer ratio of said transducer according to a moving average of the input energy, and means for reducing the lag in the operation of said control channel on decrescendo only.

16. In a sound reproducing system, a sound record, a pick-up device therefor, an amplifier fed by said pick-up device, a sound propagating device said pick-up device, said control circuit having a biasing resistance and a rectifier for passing a subaudio biasing current through said resistance to control the gain ratio of said amplifier, a timing capacitance associated with said resistance to determine the length of interval over which the signal is averaged to obtain said sub-audio current, a discharge circuit for said capacitance, and means for controlling said discharge circuit in such manner that change in signal strength changes the impedance of said discharge circuit.

17. In a sound reproducing system, a sound record, a pick-up device therefor, an amplifier fed by said pick-up device, a sound propagating device fed by said amplifier, a control circuit fed by said pick-up device, said control circuit having a biasing resistance and a rectifier for passing a sub-audio biasing current through said resistance to control the gain ratio of said amplifier, a timing fed by said amplifier, a control circuit fed by capacitance associated with said resistance to determine the length of interval over which the signal is averaged to obtain said sub-audio current, a three element discharge tube providing a discharge circuit for said capacitance, and means for controlling the grid of said discharge tube by the intensity of the signal in such manner that decrease in signal reduces .the impedance of the discharge tube to cause said capacitance to discharge more quickly.

18. In a system for reproducing sound from a JOHN HAYS HAMMOND, JR. 

